1. Field of the Invention
The present invention relates to a control apparatus for a copying machine or the like and, more particularly, to a control section for controlling a light amount of a light source which emits light upon supply of current thereto.
2. Description of the Prior Art
Power control of a halogen lamp for original exposure in a copying machine or the like is conventionally performed by phase control using a lamp regulator (CVR). A CVR is complex in circuit configuration and is large in size. Moreover, when the power source voltage varies, the turn-on voltage of a halogen lamp also varies, as shown in FIG. 1. Referring to FIG. 1, curve I represents a power source voltage, and curve II represents a turn-on voltage of a halogen lamp. As may be seen from this graph, since the turn-on voltage of the halogen lamp varies with a change in the power source voltage, when a halftone image is reproduced, a reproduced copy image has an irregular density.
In order to turn on a light source so it produces a desired light amount, a voltage to be applied to the light source must be converged to a desired value within a short period of time. However, if a correction for converging the voltage is performed in the same manner under varying conditions, correction may be time-consuming and correct convergence may not always be achieved.
When turn-on and off of the light source are repeatedly performed, if light amount control is performed from the initial state for each turn-on operation, the time needed for converging the turn-on time is required for each turn-on operation.
When another or other loads must be driven with the same power source as that for driving the light source, the ON/OFF state of the load influences the application voltage on the light source, so that a desired light amount may not be obtained.
When the light source is energized abruptly, the light source is degraded or damaged, resulting in inconvenience. A control method may be adopted wherein a turn-on voltage is gradually increased after the turn-on operation is started. However, if repeated turn ON/OFF operations are performed with this control method, the control operation is time-consuming.
Furthermore, when this control operation is performed in the same manner from the initial state for each turn-on operation, the convergence time for achieving a desired light amount is long.
When a copy is to be reproduced with a different magnification from an original, the image density may vary in accordance with a selected magnification.
Even if the original exposure is performed with a predetermined light amount in a copying machine or the like, an optimal image may not be obtained depending upon the image state of the original.